please add a link to a picture and I'll edit it into your answer for you. Well done +1
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fossfreedom♦Oct 24 '11 at 20:52

Junjie W is right, in this folder if you replace launcher_bfb.png you replace the logo. It, may look like a transparent file but it is actually white with opacity. The background and edges are also in there.
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Lewis GoddardOct 24 '11 at 20:57

Ubuntu 12.04LTS

Unity 5, the Unity version used in Ubuntu 12.04LTSPrecise Pangolin, doesn't have support for theming Unity Dash and Launcher. However, you can still alter it's appearance by replacing Unity's image assets. This is an unsupported and unofficial method and is more of a hackish/modding way. But as of now, it's the only way to theme Ubuntu 12.04's Dash and Launcher. The Dash Button also known as Ubuntu BFB (Big Freakin Button), can be changed by replacing the following images in /usr/share/unity/5:

If you're unable to change the Dash Button by replacing these images, it's highly likely that your Ubuntu is running Unity2D desktop instead of Unity.Unity2D is an alternate desktop used in Ubuntu 12.04LTS for low-end systems that cannot run the real Unity. Unfortunately, Unity2D doesn't use assets from /usr/share/unity, except for the BFB Logo. To mod Unity2D, replace /usr/share/unity/launcher_bfb.png (for changing BFB Logo/Dash Button logo) along with these files in /usr/share/unity-2d/shell/launcher/artwork:

Ubuntu logo in Unity Dash Button

If you wanna change only the Ubuntu 'Circle of Friends' (CoF) logo (BFB Logo) in Dash Button, just replace launcher_bfb.png with an image of similar dimensions. I've collected some icons from various sources like icon packs (Numix, Nitrux, Moka, Faenza and Malys), Numix GTK theme, Ubuntu Design website, Ubuntu 14.04LTS"Trusty Tahr"'s Unity 7.2, Ubuntu 12.04LTS"Precise Pangolin"'s Unity 5, etc and made them available as a single mod pack. You can download it here: